1. Field of the Invention
The present invention relates to a semiconductor apparatus in which a main current of a semiconductor device flows on the wiring pattern formed on an insulation board.
2. Description of the Related Art
In a semiconductor module in which a plurality of semiconductor devices are enclosed in a case, especially in a power semiconductor module in which a relatively large current flows, it is necessary to reduce the resistance of a wiring pattern between an electrode and an external electrode through which the main current of a semiconductor device flows.
For example, in a conventional semiconductor module 11 shown in FIG. 1, a heat spreader 14 is soldered to a copper pattern 13 formed on an insulation circuit board 12, and a semiconductor chip 15 is loaded on to the heat spreader 14. An end of an external electrode 17 is soldered to the copper pattern 13, and the external electrode 17 and an external electrode S 18 are insulated by an insulator 19.
In the semiconductor module 11 shown in FIG. 1, for example, a drain current from the external electrode 17 flows through the copper pattern 13, passes through the heat spreader 14, and enters the drain electrode of the semiconductor chip 15.
When the semiconductor chip 15 is coupled to the external electrode 18 through wire bonding 16, the constraint of the bonding operation can possibly require a predetermined distance between the external electrode 18 and the semiconductor chip 15. Generally, since the copper pattern 13 is thin (for example, about 0.07 mm), the heating value of the copper pattern 13 becomes large due to the current flowing through the copper pattern 13 when the distance between the external electrode 17 and the semiconductor chip 15, that is, the wiring length, becomes longer.
To suppress the heat of the copper pattern 13, the width (vertical length indicated by the arrow shown in FIG. 1) of the copper pattern 13 has been increased to get a larger cross-sectional area as shown in the figure (top perspective view) of the semiconductor module 11 shown in FIG. 1. That is, the width in the direction normal to the direction of the flow of the drain current is increased to obtain a larger cross-sectional area of the current path of the drain current.
FIG. 2 shows the structure of another semiconductor module 21 in which the heat of the copper pattern 13 due to the main current is suppressed.
In the semiconductor module 21, an external electrode 22 is extended to the position below the semiconductor chip 15.
As shown in the right side view in FIG. 2, the dimension of the side opposite the semiconductor chip 15 of the external electrode 22 is longer, and the semiconductor chip 15 is fixed to it by solder, etc.
In this case, the drain current flowing from the external electrode 22 enters the drain electrode of the semiconductor chip 15 from the external electrode 22 below the semiconductor chip 15. Since the external electrode 22 can be thicker than the copper pattern 13, the cross-sectional area of the current path can be increased by the above-mentioned structure, thereby suppressing the heat of the copper pattern 13.
The patent literature 1 discloses the structure of providing a metal frame 2 in which a semiconductor device loaded unit 2a and a main electrode terminal 2b are incorporated into one unit, a semiconductor device 4 is soldered to the semiconductor device loaded unit 2a, and the main electrode terminal 2b is bent and led outside.
The invention described in the patent literature 1 also has the main current flowing through the metal frame 2, thereby also suppressing the heat of the conductor pattern formed on the insulation board.
[Patent Literature 1] Japanese Patent Publication No. Hei 8-17188 (FIG. 1).
However, as shown in FIG. 1, when the cross-sectional area is increased by enlarging the width of the copper pattern 13, there is the problem that the outer dimensions of the semiconductor module 11 are increased.
Furthermore, as shown in FIG. 2, with the structure of loading the semiconductor chip 15 on to the external electrode 22, the width of the copper pattern 13 can be smaller, but it is necessary to increase the outer dimensions of the external electrode 22 formed by copper, etc. so that the entire semiconductor chip 15 can be loaded. As a result, there is the problem that the cost of parts becomes higher.